Waste water loaded with ammonium, including highly loaded industrial waste water, can be purified in different ways. In the case of physical purification, the pH value is increased by the addition of lye, whereupon ammonia is removed by stripping with steam or with a gas and recovered by condensation. The profit from the recovered ammonia is very small in comparison with the high investment costs, and, in addition, waste waters can only be purified if they contain less than 100 mg NH4-nitrogen (NH4—N) per liter in this way.
A chemical process for removal is based on the precipitation of magnesium ammonium phosphate. In this case magnesium salts and phosphates are added to the waste water, magnesium ammonium phosphate precipitates out at a specific pH value. The magnesium ammonium phosphate can be reprocessed by heating, producing magnesium hydrogen phosphate and ammonia, which can be removed by stripping. The magnesium hydrogen phosphate then can be added to the waste water again as a precipitation agent. However, this process is very cost-intensive.
A further, more economical, biological process includes treating of the waste water with nitrifying microorganisms (nitric bacteria), the nitric bacteria being colonized on a solid carrier bed. The waste water is aerated, the nitric bacteria oxidizes the ammonium nitrogen to nitrite (Nitrosomonas) or to nitrate (Nitrobacter).
Formerly the solid carrier bed for this process in general, contained lava, while more recently, in general, plastic bars, balls, or fibers have been used. These materials create a colonization surface for the nitric bacteria.
A three-stage fluidized bed reactor, in which the biomass is colonized on a carrier substance (basalt), is presented in article No. 20 by J. Mihopulos, “Cost-reducing Strategies for Water Treatment Plants: Separate Turbid Water Treatment” in the book “Sticksoffrückbelastung—Stand der Technik 1996/1997—zukünftige Entwicklungen” (“Nitrogen reloading—State of the Art 1996/1997—Future Developments”) by J. St. Kollbach and M. Grömping, TK-Verlag Karl Thomé-Kozmiensky. This substance is held in suspension with recirculation. However, the carrier substance is fairly large-grained. In addition, its specific surface is below 10 m2/g. If the aeration stops, the carrier substance is precipitated, thus leading to blockage and death of the biofilm.
A process for nitrogen removal in water treatment plants with a biological treatment stage, partial flows of the sludge treatment highly loaded with ammonium being used for growing nitric bacteria, is known from “Korrespondenz Abwasser”, 12, 1994, p. 2261-2268. The active biomass obtained is used for promoting the nitrification in the subsequent purification stages. The use of nitric bacteria in the presence of aluminum and iron hydroxides is supposed to lead to a significant elimination of nitrogen in the treated waste water during the nitrification phase. Also, a considerable amount (67%) of the nitrogen loading already should be removed from the partial flows used for growing the nitric bacteria. In addition, the metal hydroxides loaded with nitric bacteria are removed with the sludge and can lead to environmental pollution as they easily release the corresponding trivalent cations.